单项选择题

执行下面的程序，消息框里显示的结果是______。
Private Sub Form_Click()
Dim Str As String, S As String, k As Integer
Str="abc"
S=Str
For k=Len(Str) To 1 Step -1
S=S & (Mid(Str,k,1))
Next k
MsgBox S
End Sub

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